Effect of rocket exhausts on infrared planet sensors.

Abstract

Infrared trackers can incur serious errors when viewing a planet through the exhaust plume of a rocket engine. Quantitative prediction involves the evaluation of the distribution of plume properties, the spectral emission and absorption of the plume as a function of line of sight, and the integrated radiation power entering the tracker fields of view from both planet and plume. A numerical example of error calculations is presented for a radiation-balance tracker located on a space vehicle executing an earth-moon mission. The plume considered is that generated by a storable-propellant rocket with an exit diameter of 100 in. Tracker field angles of 5.45° to 17.3° are considered, and pointing errors are evaluated at earth ranges from 24,700 to 197,000 miles. Pointing errors up to the loss-of-track limit are encountered when the earth is viewed through the plume near the nozzle exit. The region of error is greatest for large tracker fields and large ranges. Nomenclature B = Planck function B e = rotational constant / = intensity 7co = spectral intensity M = Mach number TV = mole fraction P = pressure R = radius, or radial position R 0 = radial position of tracker S = tracker-to-plume distance T = temperature Y = axial position of tracker X = distance from nozzle exit a = integrated band absorption dp = pointing error jj. = volumetric absorption coefficient <P = plume coordinate (elevation) 5 = solid angle 6 = plume coordinate (azimuth) co = wave number